Water electrolysis system

ABSTRACT

A water electrolysis system includes a high-pressure water electrolysis apparatus, a water circulation apparatus and a vapor-liquid separation apparatus. The high-pressure water electrolysis apparatus generates oxygen and hydrogen The hydrogen has a pressure higher than a pressure of the oxygen. The water circulation apparatus circulates water to the high-pressure water electrolysis apparatus. The vapor-liquid separation apparatus separates a gas component discharged from an anode side of the high-pressure water electrolysis apparatus from the water in the water circulation apparatus. The vapor-liquid separation apparatus includes a reservoir, a blower and a movable wall. The movable wall is disposed in the reservoir. The movable wall is vertically movable in accordance with a water level in the reservoir and allows the gas component to pass therethrough.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2010-190539, filed Aug. 27, 2010.” The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a water electrolysis system.

2. Discussion of the Background

Hydrogen gas is used, for example, as a fuel gas to generate electric power with a fuel cell. In general, the hydrogen gas is produced by using a water electrolysis apparatus. The water electrolysis apparatus uses a solid polymer electrolyte membrane (ion exchange membrane) to decompose water and generate hydrogen (and oxygen). The solid polymer electrolyte membrane and electrode catalyst layers disposed on both sides thereof constitute a membrane electrode assembly. The membrane electrode assembly and an anode feeder and a cathode feeder disposed on both sides thereof constitute a unit cell.

A voltage is applied to both ends of a stack of such unit cells, and water is supplied to the anode feeder. Then, on the anode side of the membrane electrode assembly, the water is decomposed and hydrogen ions (protons) are generated. The hydrogen ions pass through the solid polymer electrolyte membrane to the cathode side and combine with electrons to generate hydrogen. On the anode side, oxygen is generated together with the hydrogen ions (protons) and the oxygen is discharged from the unit cell together with residual water.

Regarding such a water electrolysis system, Japanese Unexamined Patent Application Publication No. 9-291385, for example, describes as a water circulation unit of a water electrolysis apparatus (water electrolysis system). Referring to FIG. 5, in the water electrolysis system, an oxygen-side water tank 1 and a hydrogen-side water tank 2 are disposed above a water electrolysis cell 3, so that water is naturally supplied to the water electrolysis cell 3 through water supply pipes 4 a and 4 b due to gravity. A power supply 5 is configured to be switched on and off by a thyristor, so that the amount gas generated by electrolysis and the interval of gas generation are adjustable.

Water supply channels 6 a and 6 b for supplying water are connected to the oxygen-side water tank 1 and the hydrogen-side water tank 2, respectively. Generated gases lift water in discharge pipes 7 a and 7 b.

Because the gases are generated periodically as the power supply 5 is turned on and off, water is effectively interposed between gases, whereby a large amount of water can be lifted. To supply the amount of water that has been lifted, water is supplied through the water supply pipes 4 a and 4 b by gravity.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a water electrolysis system includes a high-pressure water electrolysis apparatus, a water circulation apparatus and a vapor-liquid separation apparatus. The high-pressure water electrolysis apparatus generates oxygen on an anode side and generates hydrogen on a cathode side by electrolyzing water. The high-pressure water electrolysis apparatus includes an electrolyte membrane and power feeders sandwiching the electrolyte membrane therebetween. The hydrogen has a pressure higher than a pressure of the oxygen. The water circulation apparatus circulates the water to the high-pressure water electrolysis apparatus. The vapor-liquid separation apparatus separates a gas component discharged from the anode side of the high-pressure water electrolysis apparatus from the water in the water circulation apparatus. The vapor-liquid separation apparatus includes a reservoir, a blower and a movable wall. The reservoir has an inlet port in a lower part thereof through which the gas component from the high-pressure water electrolysis apparatus and the water is introduced. The blower supplies dilution air to the reservoir from an upper part of the reservoir. The movable wall is disposed in the reservoir. The movable wall is vertically movable in accordance with a water level in the reservoir and allows the gas component to pass therethrough

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

FIG. 1 is a schematic view of a water electrolysis system according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of a unit cell of the water electrolysis system.

FIG. 3 is a partial perspective view of a reservoir of the water electrolysis system.

FIG. 4 illustrates the operation of the reservoir.

FIG. 5 is a schematic view of water electrolysis system described in Japanese Unexamined Patent Application Publication No. 9-291385.

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings.

Referring to FIG. 1, a water electrolysis system 10 according to an embodiment of the present invention includes a high-pressure water electrolysis unit 12, a water circulation unit 14, a vapor-liquid separation unit 16, a water supply unit 18, and a controller 20. The high-pressure water electrolysis unit 12 generates oxygen and high-pressure hydrogen (hydrogen having a pressure higher than that of oxygen) by electrolyzing water (pure water). The water circulation unit 14 circulates the water to the high-pressure water electrolysis unit 12. The vapor-liquid separation unit 16 separates gas components (oxygen gas and hydrogen gas) discharged from the high-pressure water electrolysis unit 12 from water in the water circulation unit 14, and stores the water. The water supply unit 18 supplies pure water, which has been made from commercial water, to the vapor-liquid separation unit 16.

The high-pressure water electrolysis unit 12 includes a stack of unit cells 24. At one end of the stack of the unit cells 24 in the stacking direction, a terminal plate 26 a, an insulation plate 28 a, and an end plate 30 a are arranged outward in this order. Likewise, at the other end of the stack of the unit cells 24 in the stacking direction, a terminal plate 26 b, an insulation plate 28 b, and an end plate 30 b are arranged outward in this order. The unit cells 24 are clamped between the end plates 30 a and 30 b.

Terminals 34 a and 34 b protrude from one sides of the terminal plates 26 a and 26 b, respectively. The terminals 34 a and 34 b are connected to a power supply (DC power supply) 38 through electric wires 36 a and 36 b.

Referring to FIG. 2, the unit cell 24 includes a membrane electrode assembly 42 having a disk-like shape, and an anode separator 44 and a cathode separator 46 that sandwich the membrane electrode assembly 42 therebetween. The anode separator 44 and the cathode separator 46 have a disk-like shape and is made of, for example, a carbon material or a metal plate.

The membrane electrode assembly 42 includes a solid-polymer electrolyte membrane 48, and an anode feeder 50 and a cathode feeder 52 that sandwich the solid-polymer electrolyte membrane 48 therebetween. The solid-polymer electrolyte membrane 48 is, for example, a thin film made of a perfluorosulfonate polymer that is impregnated with water.

An anode electrode catalyst layer 50 a and a cathode electrode catalyst layer 52 a are formed on both sides of the solid polymer electrolyte membrane 48. The anode electrode catalyst layer 50 a is made of, for example, a ruthenium (Ru) catalyst, and the cathode electrode catalyst layer 52 a is made of, for example, a platinum catalyst. The anode feeder 50 and the cathode feeder 52 are made of, for example, a sintered compact (porous conductor) of spherical atomized titanium powder.

In the outer peripheral portion of the unit cell 24, a water inlet manifold 56, an outlet manifold 58, and a hydrogen manifold 60 extend in the stacking direction. Water (pure water) is supplied through the water inlet manifold 56. Oxygen generated by reaction and unreacted water (mixture fluid) are discharged through the outlet manifold 58. Hydrogen generated by reaction passes through the hydrogen manifold 60.

On a surface 44 a of the anode separator 44 facing the membrane electrode assembly 42, an inlet passage 62 a that is connected to the water inlet manifold 56 and an outlet passage 62 b that is connected to the outlet manifold 58 are provided. On the surface 44 a, a first channel 64 that is connected to the inlet passage 62 a and to the outlet passage 62 b is provided. The first channel 64 is provided on an area of the surface 44 a that corresponds to the surface area of the anode feeder 50. The first channel 64 includes channel grooves, embosses, and the like.

On a surface 46 a of the cathode separator 46 facing the membrane electrode assembly 42, a hydrogen outlet channel 66 that is connected to the hydrogen manifold 60 is provided. On the surface 46 a, a second channel 68 that is connected to the hydrogen outlet channel 66 is provided. The second channel 68 is provided on an area of the surface 46 a that corresponds to the surface area of the cathode feeder 52. The second channel 68 includes channel grooves, embosses, and the like.

Sealing members 70 a and 70 b are integrally formed so as to surround the outer peripheral end portions of the anode separator 44 and the cathode separator 46. The sealing members 70 a and 70 b are made of a sealing material, a cushioning material, or a packing material, such as EPDM, NBR, a fluorocarbon rubber, a silicone rubber, a fluorosilicone rubber, a butyl rubber, a natural rubber, a styrene rubber, a chloroprene rubber, or an acrylic rubber.

Referring back to FIG. 1, the water circulation unit 14 includes a circulation pipe 72 that is connected to the water inlet manifold 56 of the high-pressure water electrolysis unit 12. A circulation pump 74 and an ion exchanger 76 are disposed along the circulation pipe 72. The circulation pipe 72 is connected to an outlet port 78 a formed at the bottom of a reservoir 78 of the vapor-liquid separation unit 16. One end of a return pipe 80 is connected to an inlet port 78 b at the bottom of the reservoir 78. The other end of the return pipe 80 is connected to the outlet manifold 58 of the high-pressure water electrolysis unit 12.

One end of a pure-water supply pipe 84, one end of a blower pipe 87, and an oxygen outlet pipe 88 are connected to the reservoir 78. The other end of the pure-water supply pipe 84 is connected to the water supply unit 18. The other end of the blower pipe 87 is connected to a blower 86 that supplies dilution air. The oxygen outlet pipe 88 serves to discharge gas components (oxygen gas and hydrogen gas) separated from pure water in the reservoir 78.

A movable wall 90 is disposed in the reservoir 78. The movable wall 90 is vertically movable in accordance with the position of the water surface WS in the reservoir 78, and allows gas components to pass therethrough. Referring to FIG. 3, the movable wall 90 includes a porous sheet 92 and a plurality of (for example, four) floats 94. The porous sheet 92 has a rectangular (, square, or circular) shape that corresponds to the shape of the reservoir 78. The floats 94 support the porous sheet 92 and float on the water surface WS. The floats 94 are made of, for example, a ferrous material (a stainless steel), titanium, or the like.

The porous sheet 92 is made of, for example, a metal mesh or a perforated metal plate. The porosity of the porous sheet 92 is set such that the pressure of gas components that are discharged from the high-pressure water electrolysis unit 12 and that pass through the porous sheet 92 from the water surface WS side toward a space SP side is higher than the gas pressure on the space SP side of the reservoir 78 to which the blower 86 supplies air.

Referring to FIG. 4, to be specific, the pressure loss ΔPH2+O2 that occurs due to the flow of oxygen that is generated by the high-pressure water electrolysis unit 12 and the flow of hydrogen that passes through the solid polymer electrolyte membrane 48 is set larger than the pressure loss ΔPALL due to the total gas flow after dilution by the blower 86 (ΔPH2+O2>ΔPALL) is performed.

Referring back to FIG. 1, one end of a high-pressure hydrogen pipe 96 is connected to the hydrogen manifold 60 of the high-pressure water electrolysis unit 12. The other end of the high-pressure hydrogen pipe 96 is connected to a high-pressure hydrogen supply unit (such as a fuel tank or a fuel cell vehicle, not shown).

The operation of the water electrolysis system 10 will be described below.

First, when activating the water electrolysis system 10, pure water, which has been generated from commercial water, is supplied through the water supply unit 18 to the reservoir 78 of the vapor-liquid separation unit 16. In the water circulation unit 14, the circulation pump 74 operates to circulate water from the reservoir 78 through the circulation pipe 72 to the water inlet manifold 56 of the high-pressure water electrolysis unit 12. The power supply 38A applies a voltage to the terminals 34 a and 34 b of the terminal plates 26 a and 26 b.

As a result, as illustrated in FIG. 2, in each unit cell 24, water is supplied through the water inlet manifold 56 to the first channel 64 of the anode separator 44, and the water flows along the anode feeder 50.

Accordingly, water is electrolyzed in the anode electrode catalyst layer 50 a, and thereby hydrogen ions, electrons, and oxygen are generated. Hydrogen ions generated by this anode reaction pass through the solid polymer electrolyte membrane 48 toward the cathode electrode catalyst layer 52 a side, and combine with electrons to form hydrogen.

The hydrogen flows along the second channel 68 formed between the cathode separator 46 and the cathode feeder 52. The hydrogen has a pressure higher than the pressure in the water inlet manifold 56, and the hydrogen flows through the hydrogen manifold 60 and is output from the high-pressure water electrolysis unit 12 through the high-pressure hydrogen pipe 96.

A fluid that is a mixture of oxygen generated by reaction and unreacted water flows in the first channel 64, and the mixture fluid is discharged through the outlet manifold 58 to the return pipe 80 of the water circulation unit 14 (see FIG. 1). The hydrogen in the second channel 68 has a pressure higher that that of the mixture fluid in the first channel 64, so that a part of the hydrogen passes through the solid polymer electrolyte membrane 48 and leaks to the first channel 64.

Unreacted water and gas components (oxygen gas and the hydrogen gas that has passed through the solid polymer electrolyte membrane 48) are introduced into the reservoir 78 and separated from each other, and the water is circulated by the circulation pump 74 through the circulation pipe 72 and the ion exchanger 76 to the water inlet manifold 56. The gas components separated from the water are diluted with dilution air supplied by the blower 86, and discharged to the outside through the oxygen outlet pipe 88.

Referring to FIG. 4, in this case, in the present embodiment, the movable wall 90, which is vertically movable in accordance with the position of the water surface WS in the reservoir 78 and allows gas components to pass therethrough, is disposed in the reservoir 78. Moreover, the pressure loss ΔPH2+O2 that occurs due to the flow of oxygen that is generated by the high-pressure water electrolysis unit 12 and the flow of hydrogen that passes through the solid polymer electrolyte membrane 48 is set larger than the pressure loss ΔPALL that occurs due to the total gas flow after being diluted by the blower 86.

Therefore, the gas components that are introduced into the lower side of the reservoir 78 pass through the porous sheet 92 to the upper side (the space SP side) of the reservoir 78. Then, the gas components are diluted with dilution air and discharged to the outside through the oxygen outlet pipe 88. Therefore, the gas components introduced into the reservoir 78 are significantly diluted and then discharged to the outside.

The dilution air supplied to the reservoir 78 does not pass through the movable wall 90 from the space SP side to the water surface WS side. As a result, the area of contact between the dilution air and the pure water in the reservoir 78 is significantly reduced, whereby dissolution of carbonate ions or the like in the pure water is prevented. Therefore, deterioration of an ion-exchange resin (not shown) of the ion exchanger 76 of the water circulation unit 14 is reliably prevented, which is economically efficient.

Moreover, the movable wall 90 is vertically movable due to the floats 94 in accordance with the position of the water surface WS in the reservoir 78. Therefore, there is no space between the water surface WS and the movable wall 90 in which a mixture of oxygen gas and hydrogen gas is retained, so that disposal of the mixture gas is not necessary.

According to the embodiment of the present invention, a water electrolysis system includes a high-pressure water electrolysis unit including an electrolyte membrane and power feeders sandwiching the electrolyte membrane therebetween, the high-pressure water electrolysis unit generating oxygen on an anode side and generating hydrogen an a cathode side by electrolyzing water, the hydrogen having a pressure higher than a pressure of the oxygen; a water circulation unit that circulates the water to the high-pressure water electrolysis unit; and a vapor-liquid separation unit that separates a gas component discharged from the anode side of the high-pressure water electrolysis unit from the water in the water circulation unit.

In the water electrolysis system, the vapor-liquid separation unit includes a reservoir having an inlet port in a lower part thereof through which the gas component from the high-pressure water electrolysis unit and the water is introduced, a blower that supplies dilution air to the reservoir from an upper part of the reservoir, and a movable wall disposed in the reservoir, the movable wall being vertically movable in accordance with a water level in the reservoir and allowing the gas component to pass therethrough.

In the water electrolysis system it is preferable that the movable wall include a porous sheet for setting a gas pressure of the gas component, the gas component being discharged from the high-pressure water electrolysis unit and that passes through the movable wall from a water surface side to a space side, at a pressure higher than a gas pressure on the space side of the reservoir to which the air is supplied from the blower.

In the water electrolysis system it is preferable that the movable wall include a float that floats on the water and supports the porous sheet.

With the embodiment of the present invention, because dilution air is supplied from an upper part of the reservoir, gas components (oxygen gas and hydrogen gas) that have been introduced into the reservoir are significantly diluted and discharged to the outside.

Moreover, the movable wall, which allows the gas components to pass therethrough, is disposed in the reservoir. Therefore, the area of contact between the dilution air and the pure water in the reservoir is significantly reduced, whereby dissolution of carbonate ions or the like in the pure water is prevented. As a result, deterioration of an ion-exchange resin in an ion exchanger of the water circulation unit is reliably prevented.

Moreover, the movable wall is vertically movable in accordance with the water level in the reservoir. Therefore, between the water surface and the movable wall, there is no space in which a mixture of oxygen gas and hydrogen gas is retained, so that disposal of the mixture gas is not necessary.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. 

What is claimed is:
 1. A water electrolysis system comprising: a high-pressure water electrolysis apparatus to generate oxygen on an anode side and generate hydrogen on a cathode side by electrolyzing water, the high-pressure water electrolysis apparatus including an electrolyte membrane and power feeders sandwiching the electrolyte membrane therebetween, the hydrogen having a pressure higher than a pressure of the oxygen; a water circulation apparatus to circulate the water to the high-pressure water electrolysis apparatus; and a vapor-liquid separation apparatus to separate a gas component discharged from the anode side of the high-pressure water electrolysis apparatus from the water in the water circulation apparatus, the vapor-liquid separation apparatus comprising: a reservoir having an inlet port in a lower part thereof through which the gas component from the high-pressure water electrolysis apparatus and the water are introduced; a blower to supply dilution air to the reservoir from an upper part of the reservoir; and a movable wall disposed in the reservoir, the movable wall being vertically movable in accordance with a water level in the reservoir and allowing the gas component to pass therethrough.
 2. The water electrolysis system according to claim 1, wherein the movable wall includes a porous sheet for setting a gas pressure of the gas component, the gas component being discharged from the high-pressure water electrolysis apparatus and passing through the movable wall from a water surface side to a space side, at a pressure higher than a gas pressure on the space side of the reservoir to which the air is supplied from the blower.
 3. The water electrolysis system according to claim 1, wherein the movable wall includes a float that floats on the water and supports the porous sheet.
 4. The water electrolysis system according to claim 2, wherein the porous sheet has a porosity to set the gas pressure of the gas component higher than the gas pressure on the space side of the reservoir. 